[dgellow]

Isn't "?" just a sugar for something like the following? That's how I think about it in my mind at least.

  // with "?"
  let v = x?;

  // without "?"
  let v = match x {
    Ok(o) => Ok(o),
    Err(e) => return Err(e), // exit current scope due to the return
  }.unwrap();

That feels like something that could be done with a macro.

[estebank]

It's more like

  let v = match x {
    Ok(o) => o,
    Err(e) => return Err(e.into()),
  };

> That feels like something that could be done with a macro.

Indeed. It used to be a macro called try!.

[dgellow]

Ah, thanks for the correction, that's better yes

[zozbot234]

Yes, that's control flow magic. It was prototyped with a macro, but failure handling comes up all the time in practical programming, and it's important to make it as ergonomic as possible.

[dgellow]

I see. I think reading your initial comment I took issue with the hyperbole "crazy control-flow (monadic) magic is happening here".

But yes it is a hidden control flow, and taking in account hidden control flows is inherently more complicated (or at least has a steeper learning curve).